The knee joint comprises the interface between the distal end of the femur and the proximal end of the tibia. In a properly-functioning knee joint, medial and lateral condyles of the femur pivot smoothly along menisci attached to respective medial and lateral condyles of the tibia. When the knee joint is damaged, the natural bones and cartilage that form the joint may be unable to properly articulate, which can lead to joint pain and, in some cases, interfere with normal use of the joint.
In some situations, surgery is required to restore normal use of the joint and reduce pain. Depending upon the severity of the damage, the surgery may involve partially or completely replacing the joint with prosthetic components. During such knee replacement procedures, a surgeon resects damaged portions of the bone and cartilage, while attempting to leave healthy tissue intact. The surgeon then fits the healthy tissue with artificial prosthetic components designed to replicate the resected tissue and restore proper knee joint operation.
One knee replacement procedure—total knee arthroplasty (“TKA”)—involves the resection of some or all of each of the medial and lateral condyles of both the femur and tibia and the removal of the fibro-cartilage menisci located at the femorotibial interface. A prosthetic femoral component, typically made of cobalt-chromium alloy or other strong, surgical-grade metal, is fitted and secured to the distal end of the femur to replace the resected portion of the femur. Similarly, a prosthetic tibial component, the base of which is also typically made of cobalt-chromium alloy, titanium, or other suitable metal, is fitted and secured to the proximal end of the tibia to replace the resected portion of the tibia.
In some situations, the patient's bone at the knee joint may have deteriorated to a point which requires TKA surgery, but one or more of the patient's cruciate ligaments (e.g., the anterior cruciate ligament (ACL) and/or posterior cruciate ligament (PCL)) are in sufficient condition to provide adequate joint stability. Maintaining the native cruciate ligaments is often advantageous, as doing so is generally thought to aid in proprioception (the ability to sense where parts of the body are in relation to each other) and could make activities like climbing stairs feel more stable or natural. Preserving the cruciate ligaments can also promote more normal front to back knee motion, which can enhance the patient's ability to maintain pre-operative range of motion, particularly as it relates to deep flexion. The ligaments also aid in joint stability.
Each of the native cruciate ligaments connects to one of the femoral condyles, passes within the intercondylar region of the femur, and connects to the center-top portion of the tibia called the tibial eminence. In order to accommodate the passage of the cruciate ligaments, the femoral and tibial implant components used in cruciate-retaining procedures typically comprise intercondylar cutaways that define a vertical passage between the intercondylar fossa of the femur and the tibial eminence. The medial and lateral components of each of the femoral and tibial prosthetic components are separated by a deep intercondylar passage (or “notch”) that allows for passage of cruciate ligaments vertically through the notch.
During normal operation of the knee joint, the cruciate ligaments can exert significant tension at the attachment site of the tibia called the tibial eminence. In a healthy knee joint, there is sufficient tissue surrounding the tibial eminence to aid in the distribution of this force across the surface of the tibia. Installation of a cruciate-retaining tibial prosthetic component, while aimed at preserving an attachment site at the tibial eminence, typically requires significant removal of the surrounding native tissue of the tibia to make way for installation of the tibial implant. Unfortunately, this surrounding tissue provides much of the attachment strength that counteracts the tension applied by the cruciate ligaments. Consequently, removal of this tissue can substantially weaken the attachment strength of the tibial eminence. One major problem associated with cruciate-retaining tibial procedures is the incidence of failure of the tibial eminence due to the removal of surrounding supporting structure that is required by the installation of the tibial prosthetic.
Early solutions for addressing the problem of tibial eminence failure were aimed at increasing the width of the intercondylar notch of the tibial prosthetic, which, in turn, increased the amount of native bone that could be preserved in the area immediately surrounding the tibial eminence. Although the increased width of the intercondylar notch increased the attachment strength of the tibial eminence, it had several drawbacks. For example, increasing the width of the intercondylar notch resulted in a corresponding increase in the width of the structure used to connect the medial base portion to the lateral base portion. This increase in width resulted in a corresponding decrease in the structural integrity of the connecting structure. Thus, while a wider intercondylar notch tended to increase the attachment strength of the tibial eminence, it led to a significant reduction in the strength of the tibial prosthetic component.
In order to increase the structural integrity of the implant, some prosthetic designs utilize a support system that comprises a network of interconnected keels provided on the underside of the implant. This support system is designed for insertion into corresponding voids in the bone that are created by the surgeon during the knee replacement procedure. Although these systems may enhance the overall strength of the implant and allow for a wider intercondylar passage, they require removal of a significant amount of subsurface tissue, which can undermine the area surrounding the tibial eminence. This may compromise the strength of the area beneath the tibial eminence, which may result in increased incidence of failure of the tibial eminence.
The presently disclosed tibial prosthetics for cruciate-retaining knee arthroplasty procedures are directed to overcoming one or more of the problems set forth above and/or other problems in the art.